The measurement of fluid flow is very important in industrial applications. Optimum performance of some equipment and operations require specific flow rates. The cost of many liquids and gases are based on the measured flow through a pipeline making it necessary to accurately measure and control the rate of flow for accounting purposes.

A Flow meter is a device used to measure the rate of fluid movement at a given point in the pipe or tube. The flow meter is usually secured to a break in the pipe and the fluid is allowed to move through it.

Types of Fluid Flow meters:
Several methods are employed to classify flowmeters. One method is to divide flowmeters into the following categories:
(a) Differential Pressure Flowmeters
(b) Mechanical Flowmeters
(c) Electronic Flowmeters
(d) Mass Flowmeters 
The different types of fluid flowmeters are used in many industrial applications to measure the flow of fluids. The flow of a fluid can be measured in many ways. Commonly used methods are a simple volumetric measurement or a rate measurement.

A volumetric flow measurement can be as simple as filling and emptying a container whose volume is known and counting the number of times it is done or a rate measurement which is performed by keeping track of the time period. 
Flow instruments measure flow using various measurement metrics. Two of the most popular measurement metrics are:
(a) Volumetric flow rate - in cubic feet, gallons, or liters per unit of time (this is an inferred measurement)
(b) Mass flow rate - pounds, tons, grams, or kilograms per unit of time.

Volumetric flow can be determined by using:
Volume Flow = Area x Velocity

If we define Volume flow = Q
Area = A, and
Velocity = V, 
Then volumetric flow can be put simply as:
Q = VA

Mass flow rate can be determined from volumetric flow as follows:
We know that, M = Volume x Density of fluid 
Therefore, Mass flow = Volume flow x Density of fluid